1. Field of the Invention
The present invention relates to an electronic component device in which a rectangular plate-shaped electronic component element having a functional part thereon is mounted on a substrate with bumps. In further detail, the present invention relates to an electronic component device in which a rectangular plate-shaped electronic component element is mounted on a substrate so that a functional part of the electronic component element is hermetically sealed. The electronic component element has a coefficient of linear expansion in the x direction along a side of the rectangle and a coefficient of linear expansion in the y direction orthogonal to the x direction in the plane of the rectangle, wherein the coefficients of linear expansion being different from each other.
2. Description of the Related Art
Hitherto, various electronic component devices in which an electronic component element (hereinafter also abbreviated to as an element), such as a SAW element or a high-frequency element, is installed on a substrate have been proposed.
For example, Japanese Unexamined Patent Application Publication No. 4-293310 discloses a surface acoustic wave device in which a SAW element is mounted on a base plate with bumps. In more detail, hot-side lands are provided on a surface of the base plate and solder bumps are provided on the corresponding hot-side lands. In addition, a frame-shaped earth-side land is provided on the surface of the base plate so as to surround the hot-side lands. A solder sealing frame is provided on the frame-shaped earth-side land. On the other hand, interdigital transducers (IDT), hot-side patterns, and earth-side patterns are provided on a surface of a SAW element chip to form a functional part. The SAW element is fixed on the base plate with a predetermined space therebetween such that the surface having the IDTs of the SAW element faces the surface of the base plate. The space is hermetically sealed with the solder sealing frame.
However, in the surface acoustic wave device described in Japanese Unexamined Patent Application Publication No. 4-293310, the coefficient of linear expansion in the x direction along a side of the rectangular plate-shaped SAW element is different from the coefficient of linear expansion in the x direction of the base plate. In addition, the coefficient of linear expansion in the y direction, which lies in the plane of the rectangle of the SAW element and is orthogonal to the x direction, is different from the coefficient of linear expansion in the y direction of the base plate. Thus, in the SAW element and the base plate, the coefficients of linear expansion in the same direction are different from each other. Therefore, when a thermal shock is applied during a reliability test or during use, a large difference in expansion is generated between the SAW element and the base plate. Consequently, a strain or a fatigue breaking is generated in the sealed portion, resulting in a sealing failure. This causes a problem that the lifetime for thermal shock resistance required for general electronic component devices cannot be satisfied.